Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
J Chem Phys. 2013 Jul 28;139(4):044313. doi: 10.1063/1.4816636.
Sumanene is a typical buckybowl molecule with C3v symmetry. We observed a fluorescence excitation spectrum and a dispersed fluorescence spectrum of sumanene in a supersonic jet. Bowl effects were clarified by comparing the spectra with those of triphenylene (D3h symmetry), which is a planar prototype of nonplanar sumanene. The S1 (1)A1 ← S0 (1)A1 transition is symmetry allowed. We found the 0(0)(0) band in the fluorescence excitation spectrum at 357.78 nm; this band was missing in the forbidden S1 (1)A1(') ← S0 (1)A1(') transition of triphenylene. The transition moment was shown to be along the oblate symmetric top axis (out of plane) by the observed rotational contour. A large number of vibronic bands were observed, unlike in triphenylene. Some were considered to be out-of-plane vibrational modes, which lead to a bowl-to-bowl inversion reaction assisted by in-plane vibrations. We found that the vibronic bands were markedly weak in the high energy region of triphenylene-d12. This indicates that the fluorescence quantum yield is very low at the high vibrational levels in the S1 state due to the rapid radiationless transition. The main process is considered to be internal conversion to the S0 state. The nonplanar structural distortion may also enhance radiationless transitions. We could not, however, observe weakening of the vibronic bands in the fluorescence excitation spectrum of sumanene.
并五苯是一种具有 C3v 对称性的典型的篮状分子。我们在超声速射流中观察到了并五苯的荧光激发光谱和分散荧光光谱。通过将这些光谱与平面原型非平面并五苯的光谱进行比较，阐明了碗状效应。S1（1）A1←S0（1）A1 跃迁是对称允许的。我们在荧光激发光谱中发现了 357.78nm 的 0（0）（0）带；而在 triphenylene 的禁戒 S1（1）A1（'）←S0（1）A1（'）跃迁中，该带缺失。通过观察到的转动轮廓，表明跃迁矩沿着扁长对称陀螺的轴（离面）。与 triphenylene 不同，我们观察到了大量的振动态。一些被认为是离面振动模式，它们通过面内振动辅助篮状到篮状的反转反应。我们发现，在 triphenylene-d12 的高能区域，振动态带显著减弱。这表明由于无辐射跃迁，在 S1 态的高振动能级上荧光量子产率非常低。主要过程被认为是向 S0 态的内转换。非平面结构变形也可能增强无辐射跃迁。然而，我们在并五苯的荧光激发光谱中并没有观察到振动态带的减弱。
